The preparation of organopolysiloxanes by hydrolysis and condensation of halosilanes is known. Organopolysiloxanes are also frequently prepared starting from mixtures of low-molecular-weight and high-molecular-weight organopolysiloxanes, which are equilibrated to give low-molecular-weight mixtures by adding a suitable catalyst. However, the latter method is not an adequate solution for preparing organopolysiloxanes with a very low degree of condensation. The known preparation processes are also particularly directed at forming cyclic organopolysiloxanes with a ring size of from 3 to 6 siloxane units.
No processes are known for directly preparing mixtures of linear low-molecular-weight siloxanes with a low proportion of hexamethyldisiloxane and of cyclic siloxanes, but the targeted products can be prepared by mixing the individual components in a very time-consuming and costly manner.
A continuous process for hydrolyzing organochlorosilanes is described in DE-C 954 198. This reaction is carried out in a loop reactor. The concentration of the discharged hydrochloric acid produced during the reaction is at least 25%. This high concentration leads to a crude hydrolysate with unhydrolyzed and undesirable Si--Cl units.